Reed switch contact construction



Oct. 3, 1967 w. M. GRENGG 3,345,593

REED SWITCH CONTACT CONSTRUCTION Filed April 25, 1966 2 Sheets-$heet l fizflentor: Maker ML 67% 723 7 Get. 3, 1967 w. M. GRENGG 3,345,593

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VIII/521111411114 United States Patent 3,345,593 REED SWITCH CONTACT CONSTRUCTION Walter M. Grengg, Madison, Wis., assignor, by mesne assignments, to Oak Electro/Netics Corp., a corporation of Delaware Filed Apr. 25, 1966, Ser. No. 545,018 14 Claims. (Cl. 335-154) This invention relates to electrical switching devices and more particularly, although in its broader aspects not exclusively, to magnetically operated switches of the type employing incapsulated flexible reeds for selectively opening and closing electrical circuit paths.

As illustrated by US. Patent No. 2,289,830, which issued to W. B. Ellwood on July 14, 1942, a magnetically operated switch may be constructed of moving reed contacts which are mounted within a hermetically sealed, evacuated or gas-filled envelope in order to prevent contact contamination or oxidation as well as to reduce the fire hazard created by open-air arcing. The reeds used in such switches are constructed of a magnetic, electrically conductive, resilient material and are flexed by an applied magnetic field to open or close an electrical circuit path. The actuating field is commonly produced by a magnetizing coil which is wound around the envelope. Commonly, a magnetic material exhibiting substantial hysteresis is used in the core of the magnetizing coil or in the reeds themselves such that the switch contacts latch in position when the coil is pulsed, opening whenever the coil is pulsed in the opposite direction.

While prior reed switches have been used to advantage in many applications, these switches have exhibited certain shortcomings. Because the resilient reeds are normally afiixed at one end only and extend cantilever-fashion to a position overlapping an associated contact member, vibration or shock may cause sufiicient reed movement to create a momentary circuit closure. To prevent this, the gap width separating the reed from the other contact member may be increased or the reed may be made less flexible. Both of these preventive measures tend to make the switch less sensitive, thus requiring a stronger applied field to accomplish switching.

, In addition, the reed must normally be capable of sufiicient return spring action to prevent the contacts from sticking due to contamination or arcing. This requirement of substantial return spring tension also lessens the sensitivity which is normally obtainable.

It is accordingly an object of the present invention to improve the sensitivity of a reed type switch while maintaining its resistance to contact sticking and the affects of shock and vibration.

As mentioned above, the gap width separating the reed from its associated contact has a profound effect upon the sensitivity of the relay. The requirement that precise contact separation be maintained also greatly increases the amount of care which must be taken during construction of conventional reed switches. Even when such care is exercised, unavoidable variations from switch to switch cause the performance of the finished products to be somewhat unpredictable.

It is accordingly a further object of the present invention to produce an easily assembled yet mechanically precise reed switch.

In a common reed switch construction, the contacting elements are bonded to conductors which are extended through and are sealed in a glass or ceramic envelope. External circuit connections are made by soldering to these extending conductors. In order to replace a reed switch which has become defective due to extended operation, it is necessary to make time consuming solder con nections. 1

It is accordingly a further object of the invention to provide an improved switch reed construction which is adapted for easy assembly within a cartridge which may be remova'bly mounted within a socket-type receptacle.

In the principal aspect, the present invention takes the form of a switching device which employs a resilient, electrically conductive, magnetizable, elongated reed for opening and closing a circuit path. The reed is mounted within an elongated hollow tube and overlaps an electrically conductive contact member which is mounted in spaced relation from the inside wall of the tube to define a gap. In accordance with a principal feature of the invention, the reed is supported along a substantial portion of its length by its resilient spring pressure which forces this portion of the reed against the inside wall of the tube.

In a preferred embodiment of the invention, the open ends of the tube are sealed by a pair of electrically conductive caps which are respectively connected to the reed and to the contact member. The reed itself is preferably bent to form bifurcated arms which bear under spring tension against opposing portions of the inside wall of the tube. In a preferred arrangement, the read is bent into a W-shape and the two bights are bonded directly to an end cap. Alternatively, the reed may be bent into a hairpinshape with its single 'bight bonded to an end cap. To simplify construction of the switch contemplated by the invention, the end caps may be pre-coated with solder or the like such that by heating the cap after the assembly, the desired bond between the reed and the associated cap may be formed.

These and other objects, features and advantages of the present invention may be more clearly understood through a consideration of the following detailed description. In this description reference will be frequently made to the attached drawings in which:

FIGURE 1 is a side, cross-sectional view of a replaceable reed switch cartridge mounted within a magnetizing solenoid;

FIGURE 2 is an exploded perspective view of the various parts which make up the embodiment of the invention further illustrated in FIGURES 3, 4 and 5;

FIGURE 3 is a side, cross-sectional view of a preferred reed switch cartridge which embodies the principles of the invention;

FIGURE 4 is an end cross-sectional view of the reed switch cartridge shown in FIGURE 3 taken substantially along the line 4-4 of FIGURE 3;

FIGURE 5 is a side view of a single reed showing its shape before and after insertion into the hollow envelope;

FIGURE 6 is a side cross-sectional view of a further embodiment of the invention;

FIGURES 7, 8 and 9 are end cross-sectional views of the switch shown in FIGURE 6 taken along the lines 77, 8-8, and 99 respectively;

FIGURES 10 and 11 are side and end cross-sectional views respectively of a third reed switch construction embodying the principles of the invention;

FIGURES 12 and 13 are side and end views respectively of a single-pole, double-throw reed switch arrangement which embodies the invention;

FIGURES 14 and 15 are side and end views respectively of a fifth embodiment of the invention employing tungsten contacts for extending the life of the switch; and

FIGURE 16 is an enlarged cross-sectional view of a portion of the reed switch cartridge shown in FIGURES 14 and 15 taken substantially along the lines 16-16 of FIG- URE 14. i

The reed switch construction contemplated by the present invention may take the form of a fuse-type cartridge as shown generally in FIGURE 1 at 20. This cartridge includes a glass or ceramic tube 22 into which the movable 3 contact elements are inserted. The ends of this hollow tube 22 are sealed by metallic end caps 23 and 24. The cartridge 20 is surrounded by a magnetizing coil shown generally at 25 and is held in a central location within the coil 25 by four similar spring members 26 through 29. Radially extending flange 31 is electrically connected with the spring members 26 and 27 while flange '32 is connected to spring members 28 and 29 to provide external terminals for the switching element. Conductors 34 and 35 provide terminal connections for the magnetizing winding 25. The

spring members 26 through 29 are bonded to an outer plastic shell shown generally at 36 which surrounds coil 25 and through which the terminal conductors 31, 32, 34 and 35 extend. The coil 25, when energized by an application of electrical potential cross terminals 34 and 35, subjects the cartridge 20 to an axially oriented magnetic field. It is, of course, to be understood that a wide variety of different magnetizing arrangements may be employed in conjunction with the cartridge-type switching element according to the invention.

FIGURES 2 through show a preferred embodiment of the invention comprising only five simple parts shown separately in the exploded view of FIGURE 2. A pair of formed reed elements shown generally at 40 and 41 are compressed and inserted within a hollow tube shown generally at 43. The, tube 43 is preferably composed of glass, ceramic, or a like non conductive material which exhibits minimum expansion and contraction due to changes in temperature. A pair of end caps shown generally at 45 and.

46 are employed to seal the ends of the tube 43. End caps 45 and 46 may be constructed from brass and are preferably provided with a film covering of solder or the like to facilitate construction.

The reeds 40 and 41 are compressed and inserted within the tube 43. The tube 43 may be evacuated or filled within an inert gas prior to sealing with the cups 45 and 46. The inner side walls of the cups 45 and 46 may be coated with a film of thermosetting resin prior to assembly in order to assure the integrity of the hermetic seal.

The reed 40, prior to insertion into the tube 43, has a generally W-shaped cross-section as shown in FIGURE 5 by the solid line. The reed 40 includes two extended arms 49 and 51 which extend from two bights 53 and 54. When inserted into the tube, the resilient reed 40' takes on the cross-sectional shape shown by the dotted line of FIG- URE 5. When inserted into the tube 43 as shown in FIG- URES 3 and 4 of the drawings, the arms 49 and 51 bear against opposing portions of theinside wall of the tube 43 along a substantial portion of their length. As shown most clearly in FIGURE 4, the extended arm 51, being flat, bears against the inner surface of the tube 43 only at its edges 55 and 56.

The reed 40 includes a double bend 58 at a point short of the'extended end 60 of the arm 49. The end portion 60 of arm 49. thus lies in a plane parallel with and spaced from the plane of the major portion of arm 49. The end portion 60 is thus located in spaced relation from the inside wall of the tube 43 to define a gap. A freeextended I end 61 of one arm 62 of the bifurcated reed 41 extends into this gap and due to its resilient spring pressure bears against the inner wall of the tube 43. The reed 41 is essentially identical to the reed 40 and includes two bights 63 and 64, a double bend 68, and a second end portion 70 which is spaced apart from the inside wall of the tube 43. The end portion 71 of the extended arm 51 of reed 40 extends intothe gap defined by the end portion 70 and a portion of the inner wall of tube 43.

The bights, 53 andv 54- are solderedtothe endcap 45-. This is convenientlydone by heatingthe cap 45 to liquify the coating of solder previously applied. End cap 46 may be solderedto the bights 6'3 and 64 of reed 41 in the same fashion.

In the embodiment of the invention shown in FIGURES 2 through 5 the end caps 45 and 46 are electrically connected by a pair of contacts when, theswitch is closedinstead of only one.to insure reliable circuit closures.

The gap width separating the contacting surfaces is precisely fixed by the novel arrangement contemplated by the invention. For example, since the long, extended arm 62 of reed 41 and the shorter extended arm 49 of reed 40 are both pressed firmly against the upper, inside wall of the envelope 43, the gap width separating the end portions 60 and. 61 is precisely determined. Should a variation occur in the inside diameter of the tube 43, the gap width is substantially unaffected since both reed ends track with the wall. Substantial spring pressure insures that shock or vibration will not cause momentary contact and prevents contact sticking by providing. a substantial return force which is greater than that of conventional reed constructions using comparable gap widths and reed dimensions. This substantial return force also suppresses arcing by providing a more rapid contact opening. The principles of the invention permit narrow air gaps between the open contacts to provide improved sensitivity.

The unique W-shape of the reeds 40 and 41 allow substantial variations in the inside diameter of the enclosing tubing 43 to occur without substantially affecting the reed tension against the inner surface of the tube at the extended ends of the reed arms. Aswill be readily appreciated, assembly of the reed switch cartridge shown in FIG- UR'ES 2 through 5 is extremely simple and requires no precision tools or manufacturing equipment.

FIGURES 6 through 9 of the drawings illustrate a second embodiment of the invention comprising a cylindrical envelope shown generally at 75, a pair of sealing end cups 77 and 78, and a pair of reed members shown generally at 80 and81. As before, these reed members are bent to form bifurcated arms which extend into the tube 75 and which are supported along most of their length by bearing against the inside walls of the tube 75 by resilient spring pressure. The reeds 80 and 81 are bonded to the end cups 77 and 78 at the bights 83 and 84 respectively. The reed 80 includes a substantially straight extended arm 86 and a second arm 87 having a bent end portion 89. Similarly the reed 81 includes a substantially straight extended arm 91 and an arm 92 having a bent end portion 94. As shown by FIGURES 7 and 9, the arms 87 and 92 which include bent end portions are substantially narrower than the arms 86 and 91. The straight arm 86 extends under the gap formed between the bent end portion 94 and the inside surface wall of tube 75. In the same manner, the bent portion 89 forms a gap with the inner side wall of the tube 75 into which the straight arm 91 extends.

Unlike the embodiment of the invention described in conjunction with FIGURES 2 through 5, the hairpin shaped reeds 80 and 81 include only a single bight each and aremore subject to changes in spring tension with variation in the inside diameter of the cylindical envelope 75. the reeds 80 and 81 are so constructed, however, that sensitivity of the switch is maintained at a substantially constant value even though the inside diameter of the cylinder may vary. Constant sensitivity is maintained by increasing the gap width as spring tension decreases. As inside diameter increases, the bent portions 89 and 94, being supported by narrower reed arms 87 and 92 re spectively, tend to move radially outward less rapidly than the wider extended arms 86 and 91. Thus, when the inside diameter of the tube increases, the spring tension tending to hold extended arms 86 and 91 against the inner surface of the tube 75 decreases while the gap width separating the inner and outer contacts increases. Thus,

sensitivity is maintained at, a substantially constant value.

105 and 106. The reed 105 includes two extended arms 110 and 111 having end portions 113 and 114 respectively which are positioned by double bends inward and away from inside wall of the tube 100 to form gaps into which extend the bifurcated arms 116 and 117 of the reed 106. According to a feature of this embodiment of the invention, the bent end section 113 is closer to the inside wall of tube 100 than is the bent section 114 thus providing a narrower gap between end portion 113 and the reed 116. The reed 116, because it is spaced closer to the end portion 113 in the open position, closes earlier when a magnetic switching field is applied than does the reed arm 117. In addition, since the reed 117 must flex further before contacting the end portion 114, its reverse spring tension is larger and reed 117 therefor tends to open before reed 116 upon termination of the applied magnetic field.'Since both the first make and the last break occur at the gap associated with the reed arm 116, substantially all contact arcing occurs across this gap. To provide a reliable device, the extended end of reed 116 and the end portion 113 may be coated with tungsten or the like to withstand the arcing. Since very little arcing occurs across the gap associated with reed 117, the end portion of reed 117 and the end portion 114 may be plated with gold or other material exhibiting low contact resistance to provide excellent conductivity for the switch. Thus, using the arrangement shown in FIGURES 10 and 11, a switch having both high reliability and high conductivity is produced.

FIGURES l2 and 13 of the drawings show a singlepole, double throw switch comprising a glass or ceramic cylindrical envelope 120, an end cap 122, a W-shaped reed member shown generally at 124, an annular metallic sleeve 126 which is inserted at one end of the tube 120, and a centrally located contact member shown generally at 128 which is supported by a ceramic insulator 130. The contact member 128 includes a contact head 132 having an elliptical cross-section as shown in FIGURE 13. The head 132 is supported by a shaft 134 which passes through the insulator 130 and is terminated by a discshaped terminal 138. The reed 124 includes extended arms 140 and 141, the arm 140 being longer than the arm 141 to provide a longer overlap for arm 140 with the elliptical head 132. The overlapping end portion of extended arm 140 is coated with a highly conductive nonmagnetic material, such as gold or silver. The overlapping end portion of extended arm 141 may also be coated with a nonmagnetic materialalthough preferably less thickly than the coating on arm 140. Because of the larger overlap of arm 140, it is drawn toward the con tact head 132 before arm 131. However, the smaller overlap between contact 132 and reed 141 provides a greater flux concentration at the gap as the applied field diminishes on release such that reed 141 is the last to break contact. This effect is enhanced by the thicker coating of nonmagnetic material on extended arm 140 which tends to free the arm 140 earlier. Thus, in the embodiment of the invention shown in FIGURES 12 and 13, the first make and the last break occur on different reed arms, thus tending to distribute arcing damage equally between the contacts to increase the life of the switching unit.

The elliptical shape of contact head 132 shown most clearly in FIGURE 13 provides a convenient and accu rate means for adjusting the gap width. By rotating the disc 138, the elliptical head 132 may be moved closer to or farther away from the reed arms 140 and 141 as desired.

The switch of FIGURES 12 and 13 possesses doublethrow action. In the de-energized position, the metallic end cup 122 is connected through both the reed arm 140 and the reed arm 141 to the metallic sleeve 126. Upon applying an axial magnetic field to the cartridge, both reed arms 140 and 141 move into the contacting engagement with the central contact member 128 to provide an 6 electrical connection between end cup 122 and the disc 138.

FIGURES 14, 15 and 16 of the drawings illustrate still another embodiment of the invention utilizing tungsten elements to increase the reliability of the switch. The cartridge shown comprises a glass or ceramic tube 150, end cups 153 and 154, a W-shaped reed element shown generally at 158, a central contact member having a frusto-conical portion and a cylindrical extended portion 162. A tungsten snap ring 163 fits into an annular groove 164 around the cylindrical contact member 162 and tungsten strips and 171 are affixed to the extended ends of reed arms 173 and 174 respectively of the reed element 158. The reed arm 173 overlaps the cylindrical contact member 162 by a greater amount than does the reed arm 174 such that the first make and the last break occur on different reeds as discussed in conjunction with FIGURES 12 and 13.

In FIGURES 14 and 16, arm 173 is shown as just having made contact with the central member 162 as the switch closes while need arm 174 has not yet contacted the central member 162. It will be noted that the tungsten reed 171, however, has already contacted the snap ring 163 such that contact is established prior to actual engagement of the reed arm 174 with the member 162. The use of the tungsten snap ring 163 and strips 170 and 171 thus provides the capability for making and breaking contact under severe loads without actual damage of the contacts which, if desired, may be gold plated.

It is to be understood that the embodiments of the invention which have been described are merely illustrative of applications of the principles of the invention. Numerous modifications may be made to these arrangements and others devised by those skilled in the art Without departing from the true spirit and scope of the invention.

What is claimed is:

1. In combination,

an elongated hollow tube,

an electrically conductive contact member mounted within said tube bearing under spring action against the inside wall of said tube and having an end portion bent outwardly from the inside wall of the said tube to define a gap,

a resilient, electrically conductive, magnetic, elongated reed mounted such that one end thereof extends into said gap, said one end being normally held in spring tension against said inside wall of said tube, and

means for producing a magnetic field within said tube to cause said reed to flex into engagement with said contact member.

2. A combination as set forth in claim 1 wherein said reed is held in spring action against the inside wall of said tube along a substantial portion of its length.

3. In combination,

a cylindrical tube,

a contact member positioned within said tube in spaced relation to a portion of the inside wall of said tube to define a gap therebetween,

an electrically conductive, magnetic, resilient reed bent to form first and second bifurcated arms and inserted into said tube such that said arms bear under spring action against opposing portions of the inside wall of said tube, one of said arms being extended into said gap, and

means for producing a magnetic field within said tube to cause said one arm to flex into engagement with said contact member.

4. The combination as set forth in claim 3 including first and second end caps for sealing the ends of said tube, means for electrically connecting said contact member to said first end cap, and means for electrically connecting said reed to said second end cap at the location of the bend in said reed.

5. A reed switch comprising, in combination,

a hollow cylindrical tube,

first and second resilient, electrically conductive, magnetic reeds, each bent to. form bifurcated arms and inserted into said tube such that the two arms, of each reed bear under springaction against opposing portions of the inside wall of said tube,

an endportion of one, arm of said first reedbeing bent outwardly from, said inside wall to form a gap between said inside wall and said bent end portion,

the extended end, portion of one arm of said second reed being positioned within said gap, and

means for producing a magnetic field within said tube to cause said one arm of said second reed to flex into engagement with saidbent end portion of said arm of said; first ree 6. An arrangement as set forth in claim 5 wherein said one arm of said second reed is substantially longer than said one arm of saidfirst reed.

7 A reed switch as set forth in claim 5 wherein said reeds are fiat and whereinsaid' one arm of said first reed is more narrow than said one arm of said second reed such that, as the inside, diameter of said tube increases, said second reedmoves radially outward a greater distance than does said first reed to increase the spacing between; said one arm of said second reed and said bent end portion'of said first reed;

8; A reed switch as set forth in claim 5 wherein each of said reeds; is W-shaped to include a pair of spacedapart bights-each, 1

9. A reed switch as set forth in, claim 5 wherein each of said reeds is U-shaped to include a single bight each.

10. A reed switch cartridge comprising, in combination,

a cylindrical, nonconducting envelope having two opened ends,

a pair of metallic caps for sealing these ends,

a resilient, bifurcated reed member having its bight rigidly affixed toone of said end caps such that the two extended arms of said reed member extend within said envelope and bear against the inside walls of a d n elope, and

a centrally located contact member aflixed to the other of said caps and extending within said envelope to a position, overlapping and spaced apart from said arms.

11. A reedswitch cartridge as set forth in claim 10 wherein said centrally located contact member has a noncircular cross-section to permit adjustment of the spac: ing between said member and saidarms byrotating said member.

12. A reed switch cartridge as set forth in claim 10 including a tungsten element mounted; on said contaetmember and a flexible tungsten strip afi'ixed to each of said arms, each of said strips being positioned to make con tact with said element before the arm to which it is affixed makes contact with said member as said arms moves toward said member,

13. In combination, a hollow tube, first and second resilient, electrically conductive, magnetic reed arms each mounted with an extended end portion thereof bearing in spring action against a portion of the inside wall of said tube, and a contact member fixedly mounted adjacent to and spaced from said end portion of each of said reed arms, said first reed arm overlapping said contact member by a greater amount than does said second reed arm 14. A combination as set forth in claim 13 wherein said extended end portion of said first reed arm is coated with non-magnetic material.

References Cited UNITED STATES PATENTS BERNARD A. GILHEANY, Primary Examiner. I. J. BAKER, RQN. ENVALL, JR., Assistant Examiners, 

1. IN COMBINATION, AN ELONGATED HOLLOW TUBE, AN ELECTRICALLY CONDUCTIVE CONTACT MEMBER MOUNTED WITHIN SAID TUBE BEARING UNDER SPRING ACTION AGAINST THE INSIDE WALL OF SAID TUBE AND HAVING AN END PORTION BENT OUTWARDLY FROM THE INSIDE WALL OF THE SAID TUBE TO DEFINE A GAP, 